Reverse resistor lookup starts with a numeric resistance and chooses a band count, tolerance, and optional temperature coefficient. The Resistor Color Code Calculator handles values such as 4.7k, 1000, and 1M automatically as you enter the ohm value. The output is an exact marking candidate for the selected format, not proof that a matching part exists in every manufacturer series.
Normalize the value
Write the value in ohms and identify a convenient significant-digit form. 4.7 kohm becomes 4,700 ohms, which can be written as 47 x 100. For a four-band part, 4 and 7 are the two digits and red supplies x100, giving yellow, violet, red. Add gold for +/- 5 percent if that is the intended tolerance.
Choose the band count
Three and four bands use two significant digits; five and six use three. For 4.70 kohm, a five-band option may use 470 x 10, producing yellow, violet, black, brown, then the tolerance band. Both sequences describe the same nominal value but imply different precision and component formats. A six-band result adds a TCR band after tolerance and uses brown by default when no TCR is supplied.
Exact-match rules
| Input | Selected format | Result |
|---|---|---|
| 4.7 kohm | 4-band | Yellow, Violet, Red, Gold |
| 4.7 kohm | 5-band | Yellow, Violet, Black, Brown, Gold |
| 4.75 kohm | 4-band | Cannot be represented exactly with two significant digits |
| 4.75 kohm | 5-band | Yellow, Violet, Green, Brown, Gold |
| 0.23 ohm | 4-band | Red, Orange, Silver, Gold |
| 0.23 ohm | 5-band | Red, Orange, Black, Pink, Gold |
| 12.3 kohm | 4-band | Cannot be represented exactly |
| 12.3 kohm | 5-band | Brown, Red, Orange, Red, Gold |
| 1.234 kohm | 5-band | Cannot be represented exactly with three significant digits |
| 0.001 ohm | 4-band | Outside the current multiplier range |
Rounding and preferred values
Many values are written with two or three significant digits, but a requested number may not map exactly to a color code or a standard preferred-value series. A reverse calculator should not silently round when the exact resistance matters. Choose a nearby stocked value only after checking the circuit calculation, tolerance, power, voltage, and purchasing requirements.
Worked reverse examples
| Value | Four-band sequence | Meaning |
|---|---|---|
| 1 kohm | Brown, Black, Red, Gold | 10 x 100, +/- 5% |
| 4.7 kohm | Yellow, Violet, Red, Gold | 47 x 100, +/- 5% |
| 10 ohm | Brown, Black, Black, Gold | 10 x 1, +/- 5% |
| 2.2 Mohm | Red, Red, Violet, Gold | 22 x 10,000,000, +/- 5% |
| 1 ohm | Brown, Black, Gold, Gold | 10 x 0.1, +/- 5% |
| 0.1 ohm | Brown, Black, Silver, Gold | 10 x 0.01, +/- 5% |
| 100 kohm | Brown, Black, Yellow, Gold | 10 x 10,000, +/- 5% |
| 1 Mohm | Brown, Black, Green, Gold | 10 x 100,000, +/- 5% |
Calculator defaults and limits
For four-, five-, and six-band reverse lookup, an empty tolerance selection defaults to gold, or +/- 5 percent. For six-band lookup, an empty TCR selection defaults to brown, or 100 ppm/K. The tool returns an error when the value is outside the supported multiplier range or cannot be represented exactly with the selected number of significant digits. It does not search inventory or select an E-series value.
Frequently asked questions
Why can 4.7 kohm have more than one code?
Different band counts use different numbers of significant digits. A four-band and five-band code can describe the same nominal value while carrying different precision conventions.
Does reverse lookup choose the closest standard resistor?
No. It returns a directly encodable candidate or reports that the exact value is not supported. Check preferred values and inventory separately.
What does a blank tolerance mean?
In the current reverse lookup, four-, five-, and six-band requests default to gold, or +/- 5 percent. This is a calculator default, not information recovered from the missing part.
Source and limits
This guide follows IEC 60062-style resistor color marking practice and the color/value conventions used in common through-hole manufacturer tables. Color decoding identifies the nominal marking; it does not prove that a particular part is genuine, undamaged, correctly installed, or available in the stated power rating.
- Use the Resistor Color Code Calculator as a reading aid, then compare the result with the component body, schematic, bill of materials, and datasheet.
- Gold, silver, faded paint, unusual spacing, and manufacturer-specific marks can create more than one plausible reading.
- Do not use a color-only result as a safety, installation, procurement, customs, or compliance decision.
Related guides
The Chart provides the color values; 4-Band Resistors explains the normal format; and Tolerance explains why a value alone is incomplete.